The present disclosure relates to a power amplification module.
The second generation mobile communication system (2G) and the third/fourth generation mobile communication system (3G/4G) are examples of wireless communication schemes used in mobile terminals. In 2G, it is required that the power of a radio frequency (RF) signal be changed in accordance with the waveform characteristics, which are stipulated by the standard, at the time of a burst operation in which data is continuously transmitted from a mobile terminal. In addition, a power amplification module, which is for amplifying the power of an RF signal, is used in a mobile terminal in order to transmit the RF signal to a base station. Therefore, it is required that gain variations be suppressed in the power amplification module in order to output an RF signal in accordance with the waveform characteristics stipulated by the standard.
For example, a radio frequency amplifier that aims to suppress gain variations that occur with changes in temperature is disclosed in FIG. 3 of Japanese Unexamined Patent Application Publication No. 11-330866. This radio frequency amplifier includes a power transistor Q1 and a control transistor Qc having a size of 1/m of that of the power transistor Q1. An RF signal input to the base of the power transistor Q1 is input to the base of the control transistor Qc via a resistor Rb/m and a resistor Rb. Changes that occur in the collector current of the power transistor Q1 with changes in temperature and so forth are reflected in the collector current of the control transistor Qc. A bias current supplied to the base of the power transistor Q1 is controlled and gain variations are suppressed by controlling a differential amplifier in accordance with changes in the collector current of the control transistor Qc.
As described above, the bias current is controlled by using a differential amplifier in order to suppress gain variations that occur with changes in temperature in the configuration disclosed in Japanese Unexamined Patent Application Publication No. 11-330866. Consequently, the circuit scale is increased.